Dryer fabric

ABSTRACT

The invention relates to a dryer fabric, which is woven of machine direction yarns ( 2 ) and cross machine direction yarns ( 3 ). The machine direction yarns ( 2 ) have free long float above at least seven cross machine yarns on a paper side (P) of the dryer fabric ( 1 ). Further, the fabric has double cloth structure having machine direction yarns in two successive layers ( 2   a,    2   b ).

BACKGROUND OF THE INVENTION

The invention relates to a dryer fabric, which is designed to be used ona dryer section of a paper machine. The dryer fabric is a wovenstructure and comprises machine direction yarns i.e. warp yarns, andcross machine direction yarns i.e. weft yarns.

The field of the invention is defined more specifically in a preamble ofthe independent claim.

Dryer fabrics, wires and screens are used on a dryer section of a papermachine. The dryer fabrics allow the paper web to be dried to be guidedthrough the dryer section. However, the known solutions have shown tocontain some disadvantages.

BRIEF DESCRIPTION OF THE INVENTION

An object of the invention is to provide a novel and improved dryerfabric.

The dryer fabric of the invention is characterized by the characterizedfeatures of the independent claim.

An idea of the disclosed solution is that flat yarns are used as machinedirection yarns, i.e. MD-yarns or warp yarns. The fabric has a doublemachine direction yarn structure, i.e. double warp system, whereby themachine direction yarns are arranged in two successive layers.Furthermore, the MD-yarns have extremely long floats at least on a paperside surface of the dryer fabric. The long float means that the MD-yarnspass over at least seven cross machine direction yarns, i.e. CMD-yarnsor weft yarns.

Further, the dryer fabric has a double-cloth structure. Then, the dryerfabric has two independent fabric layers comprising yarns of their own.However, the structure is self-stitched so that the layers of the fabricare bound together so that the machine direction yarns engage to paperside layer and to roll side layer at suitable intervals.

An advantage of the disclosed solution is that the paper side of thedryer screen is very smooth and the contact area thereof is large. Thesmooth surface prevents the marking to the product. The extensivecontact area also allows an appropriate heat transmission between thepaper web and the dryer fabric, whereby the structure provides a higherdrying power for the fabric.

The disclosed dryer fabric also provides good running properties at thedryer section of a paper machine. This is due to the fact that theamount of air conducted by a smooth-surface dryer fabric is small. Thus,the fabric may have low air transportation and good aerodynamicproperties.

In addition, the affinity, or the force keeping the web in position, isgood on a smooth dryer fabric, and thereby the fabric controls thecourse of the web also at high speeds. Another advantage of asmooth-surfaced dryer fabric is that the fabric is kept clean, and caneasily be cleaned in case it is dirtied.

The disclosed double cloth structure, or double warp structure, of thedryer fabric makes the fabric strong and stable. Machine directionelongation of the fabric may be small since the structure comprises alarge amount of machine direction material thanks to the double clothstructure. Furthermore, wear resistance of the disclosed dryer fabricmay be excellent because of the large amount of machine directionmaterial.

According to an embodiment, the dryer fabric has eight shed double clothstructure.

According to an embodiment, machine direction yarns are verticallystacked in the structure of the dryer fabric. Alternatively, the machinedirection yarns are positioned vertically one above each other, but theyhave a slight offset relative to each other.

According to an embodiment, contact area of the paper side of the dryerfabric is 50% or more. The large contact area is formed by means of longfloats of flat machine direction yarns. It has been noted that when thecontact area 50% or more, then the drying capacity is excellent.

According to an embodiment, air permeance of the dryer fabric is between90-400 cfm (cubic foot per minute) after heat treatment. The heattreatment substantially makes the fabric dense since the MD-yarns aremoved closer to each other due shrinkage of the fabric.

According to an embodiment, the cross machine direction yarns arestrongly shrinking yarns, whereby heat treatment of the dryer fabric isconfigured to cause cross direction shrinkage of the dryer fabric sothat adjacent machine direction yarns are being moved closer to oneanother. Further, the shrinkage of the cross machine direction yarn isover 10% and that after weaving the dryer fabric has shrunk by means ofheat treatment at least 10% in the cross machine direction. Theshrinking of the dryer fabric in transverse direction also increasesamount of contact area of the paper side.

According to an embodiment, thickness or caliper of the dryer fabric isbetween 1.4-1.8 mm. When the thickness is as disclosed, the dryer fabrichas needed stability and is still not too thick.

According to an embodiment, the dryer fabric has a single-layerstructure. Then, the dryer fabric has cross machine direction yarns onlyin one single layer.

According to an embodiment, cross section of the cross machine directionyarn is round or substantially round.

According to an embodiment, diameter of the cross machine direction yarnranges between 0.4 and 0.8 mm.

According to an embodiment, cross section of the machine direction yarnsis rectangular or substantially rectangular. The cross sectional shapeof the rectangular may have round edges. Further, width of the machinedirection yarn is 0.6 mm or more, and height 0.4 mm or less.

According to an embodiment, the machine direction yarns and the crossmachine direction yarns are polyethylene terephthalate (PET) yarns.PET-yarns are less expensive compared to polyphenylene sulfide (PPS)yarns, for example. The PET-yarns may comprise an additive for improvingheat resistance and stability. Thanks to the disclosed fabric structure,less expensive material may be used without hampering wear properties,stability and durability of the dryer fabric.

According to an embodiment, the dryer fabric is a flat woven fabric.Then the dryer fabric has two opposite longitudinal edges in the machinedirection and two opposite connecting ends in the cross machinedirection. The connecting ends may be fastened together duringinstallation of the dryer fabric on a dryer section.

According to an embodiment, the dryer fabric is provided with a firstseam end and a second seam end in the cross machine direction of thefabric. The seam ends are provided with connecting members forconnecting the seam ends in order to form a seam and allowing andendless dryer fabric to be formed by the seam. The dryer fabric may beflat woven and it may be provided with any kind of integrated orseparate seaming aids or connecting members for connecting the distalends together when installing the dryer fabric to a use position.

According to an embodiment, at least part of the machine direction yarnsare arranged to form seam loops at the seam ends. The machine directionyarns may then provide the dryer fabric with a strong and non-markingwarp loop seam. The seam loops may be relatively long because of thelong floats of the machine direction yarns which form the seam loops.Thanks to relatively long seam loops, installation of the dryer fabricis easy and fast. However, the long seam loops do not cause marking tothe web.

According to an embodiment, all of the machine direction yarns form seamloops at both seam ends. Seaming of such a dryer fabric is simple andfast.

According to an embodiment, at least part of the machine direction yarnsare arranged to form seam loops at the seam ends. The loops are groupedat the seam end so that two adjacent MD-yarns are arranged to form apair of long loops and following two adjacent MD-yarns are arranged toform short loops and again next two adjacent MD-yarns form two long seamloops and so on. Thus, the seam ends may comprise so calleddouble-seam-loops.

According to an embodiment, the seam ends are provided with seam spiralswhich serve as connecting members.

According to an embodiment, the dryer fabric is made by using endlessweaving technology, whereby the dryer fabric does not comprise any seamends. Instead the dryer fabric has a shape of an endless loop.

According to an embodiment, the machine direction yarns pass below atleast seven cross machine direction yarns on the roll side of the dryerfabric, thereby forming long floats on the roll side. Long floats of themachine direction yarns on the roll side surface improve wear durabilityof the dryer fabric.

According to an embodiment, the machine direction yarns have free longfloats passing at least eleven cross machine direction yarns. It ispossible that the machine direction yarns pass over fifteen, nineteen oreven several CMD-yarns on the paper side surface and/or on the roll sidesurface.

According to an embodiment, the dryer fabric has an asymmetric structureregarding the free long flow of the machine direction yarns on the papersurface side and the roll surface side. This means magnitude of thefloats may be different on the paper side surface and the roll sidesurface.

According to an embodiment, adjacent machine direction yarns have aphase shift of two cross machine yarns.

According to an embodiment, the machine direction yarns are monofilamentyarns.

According to an embodiment, the cross machine direction yarns aremonofilament yarns.

According to an embodiment, the dryer fabric has at least eight shedweaving structure. Thus, the fabric may have 8, 10, 12 or 16 shedstructure regarding its weaving pattern. Thanks to this structure, thefabric may have extremely long free floats of MD-yarns.

The above disclosed embodiments can be combined in order to formsuitable solutions provided with necessary features.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments are described in more detail in the accompanyingdrawings, in which

FIG. 1 is a schematic perspective view of a dryer fabric provided with aseam and thereby having a shape of an endless loop,

FIG. 2 is a schematic view of a dryer fabric seen from a paper sidesurface,

FIG. 3 shows schematically and seen from the cross machine direction anend portion of a feasible single layer dryer fabric provided withconnecting seam loops for allowing formation of a seam,

FIGS. 4 and 5 are schematic views of a dryer fabric provided with longfloats of machine direction yarns on a paper side surface and on a rollor machine side surface,

FIG. 6 illustrates schematically difference between a prior art solutionprovided with short floats of MD-yarns and the disclosed solutionprovided with long floats of MD-yarns,

FIG. 7 illustrates a surface of a paper side surface of a dryer fabric,

FIG. 8 illustrates a surface topography of a paper side surface of adryer fabric and potential surface contact area is shown in the Figureby using different colour, and

FIG. 9 shows an example of features and properties of a dryer fabricaccording to the disclosed solution.

For the sake of clarity, the figures show some embodiments of thedisclosed solution in a simplified manner. In the figures, likereference numerals identify like elements.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

FIGS. 1 and 2 show some basic features of a feasible drying fabric 1.The dryer fabric 1 may be a woven structure comprising machine directionyarns 2 and cross machine direction yarns 3, which are crossing eachother. The dryer fabric may be flat woven and its seam ends SE1 and SE2may be connected to each other for forming a seam S when installed on adryer section of a paper machine. The dryer fabric 1 is configured torun in the machine direction MD. The dryer fabric 1 comprises a paperside surface P against which a paper web to be dried is arranged on thedryer section. An opposite side is a roll side surface which is againstrolls and other machine elements of the paper machine.

FIG. 3 shows an end portion of a feasible single layer dryer fabric 1provided with connecting seam loops 4. A seam S is formed when opposingseam ends SE1 and SE2 are arranged against to each other so that theseam loops 4 at their ends are being interdigitated and a seam channelis formed. A connecting yarns or seam yarn 5 is inserted inside the seamchannel for connecting the seam ends SE1 and SE2.

In FIG. 3 the basic structure of the dryer fabric 1 is single layerfabric, wherein cross machine direction yarns 3 a and 3 b are in onesingle layer. The structure may comprise cross machine direction filleryarns 3 a and basic cross machine direction yarns 3 b. Yarns 3 b areconnected with the machine direction yarns 2. The machine directionyarns 2 are arranged in two layers 2 a, 2 b which are one above theother so that the yarns 2 a are running on the paper side surface P andthe yarns 2 b are running on the roll side surface R. Thus, the fabrichas double fabric structure comprising a double warp yarn system. Themachine direction yarns form seam loops at the seam ends SE1 and SE2.The machine direction yarns 2 have free long floats LFP over seven crossmachine direction yarns 3 on the paper side surface P. The roll sidesurface R may also be provided with the long floats LFR. The number ofcross machine yarns 3 passed by the machine direction yarns 2 at thelong floats may be the same or it may be different, which means that thestructure may be symmetrical or it may be asymmetric. As can be seen inFIG. 3, the dryer fabric has eight shed-weave structure, wherein themachine direction yarn 2 passes above seven CMD-yarns 3, below oneCMD-yarn 3 and continues repeating the same pattern. Let it be mentionedthat other weave patterns, allowing extremely long floats, may also beused.

FIGS. 4 and 5 show a dryer fabric 1 having a double cloth structurehaving CMD-yarns 3 in two layers. In FIGS. 4 and 5 CMD-yarns of a bottomlayer are marked with reference numeral 3 d. Further, the dryer fabric 1is provided with long floats FLP of machine direction yarns 2 on a paperside surface P, and also on the roll or machine side surface R. FIG. 4also illustrates that all the machine direction yarns 2 may have thesame weave pattern, but an adjacent MD-yarn pattern comprises a phaseshift of one or two CMD-yarn in the same direction.

FIG. 6 illustrates schematically difference between a prior art solutionprovided with short floats SF of MD-yarns 2 and the disclosed solutionprovided with long floats LF of MD-yarns 2.

FIG. 7 illustrates a surface of a paper side surface P of a dryer fabric1. In FIG. 8 it is shown a surface topography of a paper side surface Pof a dryer fabric 1. Potential surface contact area is shown in the FIG.8 by using yellow colour. The yellow or lighter colour indicates thepotential contact surface areas whereas red or darker colour indicatesnon contacting areas. As can be easily noted from FIG. 8, the contactareas represent over 50% of the total surface of the dryer fabric 1.

FIG. 9 shows an example of features and properties of a dryer fabricaccording to the disclosed solution.

Both the MD-yarns and CMD-yarns may be monofilaments and are made ofplastic material. Flat threads are used as MD-yarns, the cross sectionof which preferably resembles a rectangle with rounded corners. Such athread is provided with a larger contact area compared, for example,with flat oval-shaped threads, which can basically also be applied. Thecross section of the CMD-yarns may, in turn, be substantially round, inwhich case the MD-yarns run as smoothly as possible between theCMD-yarns, when passing between paper side P and roll side R of thefabric. Extremely strongly shrinking threads may be employed as theCMD-yarns, meaning that the longitudinal shrinkage of an individualthread is at least 10%. Furthermore the shrinkage in the width directionof the entire dryer fabric is at least 10%.

This application relates to a dryer fabric used on a dryer section of apaper machine. However, it has been noted that the disclosed fabricstructure could also be utilized in filtering devices such as inhorizontal belt filters. The disclosed structure may also be beneficialto be used as a conveyor belt in paper machine or in any other machinewhich processes fibre web.

The drawings and the specification associated thereto is merely intendedto illustrate the idea of the invention. The details of the inventionmay vary within the scope of the claims.

1-8. (canceled)
 9. A dryer fabric for a dryer section of a papermachine, the dryer fabric (1) being a woven structure and comprising: apaper side surface (P) that is facing towards a fiber web to be driedduring use of the dryer fabric (1); a roll side surface (R) that isfacing towards the paper machine during use at the dryer section; aplurality of machine direction (MD) yarns (2), each of the plurality MDyarns (2) having a flat cross section; and a plurality of cross machinedirection (CMD) yarns (3), wherein: the dryer fabric (1) has a doublemachine direction yarn structure comprising MD yarns (2) in twosuccessive layers (2 a, 2 b); the MD yarns (2) pass above at least sevenof the plurality of CMD yarns (3) on at least the paper side (P) of thedryer fabric (1), thereby forming long floats (LF, LFP) on the paperside surface (P) and providing the dryer fabric (1) with a smoothsurface on the paper side surface (P) for preventing generation ofmarkings to the fiber web; and the dryer fabric has a double-clothstructure so that the fabric has two independent fabric layers one abovethe other, the fabric layers being self-stitched to connect the fabriclayers together.
 10. The dryer fabric as claimed in claim 9, wherein acontact area of the paper side surface (P) of the dryer fabric (1) is50% or more.
 11. The dryer fabric as claimed in claim 9, wherein: theCMD yarns (3) are strongly shrinking yarns, whereby heat treatment ofthe dryer fabric is configured to cause cross direction shrinkage of thedryer fabric so that adjacent MD yarns (2) are being moved closer to oneanother; and the shrinkage of the CMD yarn (3) is over 10%; and afterweaving, the dryer fabric (1) has shrunk by means of heat treatment atleast 10% in the cross machine direction.
 12. The dryer fabric asclaimed in claim 9, wherein: the flat cross section of the MD yarns (2)is rectangular or substantially rectangular; a width of the MD yarn (2)is 0.6 mm or more; and a height of the MD yarn (2) is 0.4 mm or less.13. The dryer fabric as claimed in claim 9, wherein the MD yarns (2)pass below at least seven of the plurality of CMD yarns (3) on the rollside surface (R) of the dryer fabric (1), thereby forming long floats(LFT) on the roll side surface (R).
 14. The dryer fabric as claimed inclaim 9, wherein the MD yarns (2) have long free floats (LF, LFP, LFR)passing over at least eleven of the plurality of CMD yarns (3) on atleast one surface of the dryer fabric (1).
 15. The dryer fabric asclaimed in claim 9, wherein the dryer fabric has at least eight shedweaving structure.